There exists today an extensive literature on the properties, activities, and uses of polysaccharides that consist, in part, of p-GlcNAc. A class of such materials has been generically referred to as "chitin", while deacetylated chitin derivatives have been referred to as "chitosan". When these terms were first used, around 1823, it was believed that chitin and chitosan always occurred in nature as distinct, well-defined, unique, and invariant chemical species, with chitin being fully acetylated and chitosan being fully deacetylated compositions. It was approximately a century later, however, before it was discovered that the terms "chitin" and "chitosan" are, in fact, very ambiguous. Rather than referring to well-defined compounds, these terms actually refer to a family of compounds that exhibit widely differing physical and chemical properties. These differences are due to the products' varying molecular weights, varying degrees of acetylation, and the presence of contaminants such as covalently bound, species-specific proteins, single amino acid and inorganic contaminants. Even today, the terms "chitin" and "chitosan" are used ambiguously, and actually refer to poorly defined mixtures of many different compounds.
For example, the properties of "chitins" isolated from conventional sources such as crustacean outer shells and fungal mycelial mats are unpredictably variable. Such variations are due not only to species differences but are also due to varying environmental and seasonal effects that determine some of the biochemical characteristics of the "chitin"-producing species. In fact, the unpredictable variability of raw material is largely responsible for the slow growth of chitin-based industries.
No reports exist today in the scientific literature describing the isolation and production, from material sources, of pure, fully acetylated p-GlcNAc, i.e., a product or products uncontaminated by organic or inorganic impurities. While McLachlan et al. (McLachlan, A.G. et al., 1965, Can. J. Botany 43: 707-713) reported the isolation of chitin, subsequent studies have shown that the "pure" substance obtained, in fact contained proteins and other contaminants.
Deacetylated and partially deacetylated chitin preparations exhibit potentially beneficial chemical properties, such as high reactivity, dense cationic charges, powerful metal chelating capacity, the ability to covalently attach proteins, and solubility in many aqueous solvents. The unpredictable variability of these preparations, as described above, however, severely limits the utility of these heterogenous compounds. For example, the currently available "chitins" and "chitosans" give rise to irreproducible data and to unacceptably wide variations in experimental results. Additionally, the available preparations are not sufficiently homogenous or pure, and the preparation constituents are not sufficiently reproducible for these preparations to be acceptable for use in applications, especially in medical ones. Thus, although extremely desirable, true, purified preparations of chitin and chitosan, whose properties are highly reproducible and which are easily manufactured, do not currently exist.